The onset of the southwest monsoon this year could well be the earliest since 2010, as per conditions on Wednesday, 21 May, weather officials said.

According to the India Metrological Department (IMD), the normal date for the onset over Kerala, which marks the beginning of the four-month-long southwest monsoon season over the country, is 1 June.

As the monsoon winds strengthen, the monsoon advances into the remaining parts of the country through June and covers the entire country by mid-July.

The IMD had earlier predicted that the onset this time could be 27 May, plus or minus four days.

But on Tuesday, 20 May they further pointed out that it could well happen during the coming four to five days and if it does, then the onset could well be the earliest since 2010.

However, on Wednesday, the IMD has gone a step further as the prescribed criterion set for the declaration of the monsoon's onset over Kerala has been technically met.

The four criteria include that 60 per cent of the 14 enlisted weather stations should report rainfall of 2.5 mm or more for two consecutive days.

 Then it has to ensure that the depth of westerlies should reach up to 600 hPa and the zonal wind speed over a designated area should be of the order of 15–20 knots at 925 hPa besides the outgoing long wave radiation value, measured in watts per square metre (wm-2), should be below 200 wm-2 in a defined area.

The IMD has warned of heavy rainfall across Kerala, Tamil Nadu, Puducherry, Karaikal, the Konkan region, Goa, central Maharashtra, Telangana, Andhra Pradesh, Bihar, Jharkhand, Manipur, Mizoram, and Tripura till 24 May.

 The IMD has also advised the fishermen not to venture into the sea from Wednesday till Monday along the coast of East-central and Southeast Arabian Sea and along and off Kerala, Karnataka, Konkan & Goa and adjoining south Gujarat coasts and Lakshadweep area.